From the viewpoint of many conservative American citizens at the time, the suppression of radicalism and radical organizations in the United States was a struggle against a dangerous subversive element controlled by a foreign power that posed a real danger to the security of the country, thus justifying extreme, even illegal measures. From a radical viewpoint it was probably seen as class warfare, particularly by the actual communists targeted. From the viewpoint of people who were caught up in the conflict for simply being objectionable (but certainly not communist spies), it was a massive violation of civil and Constitutional rights.

Another major element of McCarthyism was the internal screening program on federal government employees, conducted by the FBI under J. Edgar Hoover. This comprehensive program vetted all federal government employees for Communist connections, and employed evidence provided by anonymous sources whom the subjects of investigation were not allowed to challenge or identify. From 1951, the program's required level of proof for dismissing a federal employee was for "reasonable doubt" to exist over their loyalty; previously it had required "reasonable grounds" for believing them to be disloyal.

The hearings conducted by Senator Joseph McCarthy gave the Red Scare the name which is in common usage, but the "Red Scare" predated McCarthy's meteoric rise to prominence in 1950 and continued after he was discredited by a Senate censure in 1954, following his disastrous investigation into the U.S. Army, which started on April 22 of that year. McCarthy's name became associated with the phenomenon mainly through his prominence in the media; his outspoken and unpredictable nature made him ideal as the figurehead of anticommunism, although he was probably not its most important practitioner.

Hollywood and the entertainment industry in general came under particular fire from McCarthy and his allies. Charlie Chaplin was one person accused of un-American activities, and the FBI was involved in arranging to have his re-entry visa cancelled when he left the United States for a trip to Europe in 1952. In effect, his American film career was over even though he had not been found guilty of any offence. Walt Disney worked closely with the FBI at this time (and is described in FBI files as a "Special Agent contact"), but himself came under suspicion at one stage. His testimony before the House Un-American Activities Committee on October 24, 1947, was mainly used to denounce people in his company who he probably felt were or might become commercial threats to his operations. In addition, a group of Hollywood filmmakers who came to be known as the Hollywood Ten refused to cooperate with the investigations and were subsequently sent to prison.

The most publicly visible elements of McCarthyism were the trials of those accused of being communist agents within the government. The two most famous trials were those of Alger Hiss (whose trial began before McCarthy started brandishing his lists, and who was not convicted directly of espionage, but of perjury) and of Ethel and Julius Rosenberg, who were executed for handing over American nuclear secrets to the Soviets. Such trials typically relied on information from informers and accomplices, such as Whittaker Chambers (whose testimony led to the downfall of Hiss) and the three co-conspirators whose confessions and testimony were vital to the Rosenberg trial, Klaus Fuchs, Harry Gold and David Greenglass. By giving the names of others involved in communism, people like Chambers were able to take advantage of the system. Informants were treated less harshly than those who denied charges against them.

McCarthy's anticommunist crusade faltered in 1954 as his hearings were televised, for the first time, allowing the public and press to view first-hand his controversial tactics. The press also started to run stories about how McCarthy ruined many people's lives with accusations that were in some cases not sufficiently backed up by evidence. Famously, he was asked by the chief attorney for the Army, Joseph Welch, "Have you no sense of decency, sir, at long last? Have you left no sense of decency?" McCarthy suffered a backlash in public opinion and was investigated and then censured by the Senate for not cooperating with the investigating committee and for publicly calling them the "involuntary agent" and the "attorneys-in-fact" of the Communist Party. After the censure, McCarthy lost his other committee chairmanship, and reporters stopped filing stories about his claims of continuing communist conspiracies. He faded from the spotlight overnight. McCarthy died in office of liver failure, probably caused by alcoholism, in 1957.

McCarthyism as a generic concept

Since the time of the red scare led by Joseph McCarthy, the term McCarthyism has entered the American vernacular as a general term for the phenomenon of mass pressure, harassment, or blacklisting used to instill conformity with prevailing political beliefs. The act of making insufficiently supported accusations or engaging in unfair investigatory methods against a person as a purported attempt to unfairly silence or discredit them is often referred to as McCarthyism. The Arthur Miller play "The Crucible", written during the McCarthy era, used the Salem witch trials as a metaphor for the McCarthyism of the 1950s, suggesting that the process of McCarthyism-style persecution can occur at any time and place. The novel Fahrenheit 451 by Ray Bradbury (1953) addresses the general theme as well. Senators like John Stennis, Ralph Flanders, J. William Fulbright, John Sherman Cooper,Samuel James Ervin, and Allen J. Ellender were key senatorial figures in bringing down McCarthy.

Accusations of McCarthyism are often made by both liberals and conservatives against their political opponents for allegedly persecuting people for political reasons. For instance, conservatives often say that the "fact" that there are few politically conservative faculties in American universities is the result of McCarthyism by what they see as the liberal university establishment. On the other hand, many conservatives dislike the term because it appears to them to legitimize and perpetuate the scorn that US liberals traditionally had for McCarthy's anticommunist and anti-espionage activism, which they regard as a wise and proper thing under the circumstances.